National Flood Hazard Layer Data
Chase Dawson, Michele Claibourn
11/25/2021
Data Source
- The data represented here come from FEMA’s National Flood Hazard Layer, containing current effective flood hazard data, as downloaed through FEMA Flood Map Service Center.
- The current data was downloaded in November 2021; the NFHL is being revised continuously.
Variable Descriptions and Summaries
Variables include:
## Rows: 50
## Columns: 7
## $ GEOID <chr> "51109950202", "51109950300", "51079030200", "51079030102", …
## $ area_0 <dbl> 205.412595, 514.588394, 134.848897, 253.775954, 8.605687, 34…
## $ area_1per <dbl> 16.389151, 35.367836, 8.618762, 14.870029, 0.691124, 11.9287…
## $ area_2per <dbl> NA, NA, NA, NA, 0.107866, 0.355381, 0.134962, 0.818826, 0.31…
## $ perc_0 <dbl> 92.53404, 93.51768, 93.99951, 94.46401, 91.50433, 96.58924, …
## $ perc_1per <dbl> 7.382967, 6.427502, 6.007905, 5.535129, 7.348727, 3.304043, …
## $ perc_2per <dbl> NA, NA, NA, NA, 1.14693997, 0.09843366, 0.08842507, 0.849198…- GEOID: geographic identifer for spatial area (tracts, block groups, and blocks)
- area_0: area (in km^2) of block/block group/tract/county that do not intersect with 100-year or 200-year floodplains, or areas with minimal chance of flooding.
- area_1per: area (in km^2) of block/block group/tract/county that intersects with 100-year floodplain, or areas with a 1% annual chance of flooding.
- area_2per: area (in km^2) of block/block group/tract/county that intersects with 100-year floodplain, or areas with a 2% annual chance of flooding. This zone is also used to designate base floodplains of lesser hazards, such as areas protected by levees from 100-year flood, or shallow flooding areas with average depths of less than one foot or drainage areas less than 1 square mile.
- perc_0: percentage of block/block group/tract/county that does not overlap with the 1% or 2% annual flood zone.
- perc_1per: percentage of block/block group/tract/county that overlaps with the 1% annual flood zone.
- perc_2per: percentage of block/block group/tract/county that overlaps with the 2% annual flood zone.
5-number summaries of variables by block groups:
##
## Summary Statistics
## ========================================
## Statistic Mean St. Dev. Min Median Max
## ----------------------------------------
## area_0 54.2 71.1 0.3 16.0 358.0
## area_1per 4.4 5.7 0.0 2.0 26.8
## area_2per 0.2 0.3 0.0 0.1 2.0
## perc_0 93.2 6.7 64 94.2 100
## perc_1per 7.0 5.7 0.0 6.3 29.1
## perc_2per 0.8 1.5 0.0 0.2 7.8
## ----------------------------------------Visual Distributions
Tracts
Percent of tract in minimal flood, 1% annual floodplain, and 2% annual floodplain zones 
Block Groups
Percent of block group in minimal flood, 1% annual floodplain, and 2% annual floodplain zones 
Blocks
Percent of block in minimal flood, 1% annual floodplain, and 2% annual floodplain zones 
Maps
1% Annual Flood Zone
Tracts
Block Groups
Blocks
Block level maps are slow to render and may be added later.
2% Annual Flood Zone
Tracts
Block Groups
Blocks
Block level maps are slow to render and may be added later.